The Common Vein Copyright 2007

Ashley Davidoff MD

 

Aortic dissection is a sudden catastrophic disruption of the aortic wall caused by a shearing tear of the intima, and seconday involvement of the media by the advancing dissection and hematoma. hHe event characterised by a splitting of the arterial wall along the the longitudinal plane of the aorta.

Causative Factors

There is usually associated disease of the media in the form of cystic medial necrosis or the aging process. Familial entities such as Marfan’s syndrome, Ehlos Danlos, are associated with a significant increase of risk for aortic dissection. Entities that increase wall stress such as congenital bicuspid aortic valve, coarctation and hypertension are other factors that contribute to an increase in the incidence of the dissection. Pregnancy in the third trimester also has an increase incidence in dissection presumably due to the changes that occur to collagenous ligaments in pregnancy. About 50% of aortic dissections that occur in women under 40 are in women who are pregnant. Aortic dissection affects men more than women (2:1) with peak incidence in 6th and 7th decades.

Classification

Debakey Classification Type I – ascending aorta, extends beyond the arch Type II – confined to the ascending aorta Type III – originating in the descending aorta and usually propagates distally Type IIIa – confined to thorax Type IIIb – extends beyond diaphragm Type III dissections rarely extend retrograde to the arch

Pathology

95% of dissections occur within a few cms of the aortic valve in the ascending aorta or just distal to the left subclavian artery. There have been two classification systems with the Stanford system being more universally used. DeBakey: I ascending aorta extending to the arch +/- descending aorta (30%) II ascending aorta only (20%) III descending aorta involving the thoracic aorta (50%) Stanford: A involvement of ascending aorta B aortic arch + distal aorta

Ascending Aortic Dissection

13411b03 artery thorax thoracic ascending aorta dx aneurysm ruptured thoracic aneurysm grosspathology Davidoff MD

Dissection

This pathological specimen shows an aortic dissection starting at the root of the aorta and extending across the arch and into the descending portion. The false lumen is filled with clotted blood. Courtesy Henri Cuenoid MD 13421 code CVS thorax AO aorta dissection grosspathology

Diagnosis

Aortic Dissection

Aortic dissection is a sudden catastrophic disruption of the aortic wall caused by a shearing tear of the intima and secondary involvement of the media by the advancing dissection and hematoma. The event is characterized by a splitting of the arterial wall along the longitudinal plane of the aorta.

Aortic dissections usually occur as a result of hypertension and are formed after the intima of the aorta ruptures, leading to entry of blood into the aortic wall. Initiating tears are most frequent in the ascending aorta, though the ascending aorta is not the most commonly involved portion of the aorta regarding dissecting aneurysms. The proximal portion of the descending thoracic aorta is the second most common location of a primary intimal tear but because most ascending aortic dissections extend to involve the descending portion and because few primary tears in the descending aorta extend retrograde to the ascending aorta, the descending aorta is the most commonly involved portion of the aorta with dissecting aneurysms.

There is usually associated disease of the media in the form of cystic medial necrosis or the aging process. Familial entities such as Marfan syndrome and Ehlos Danlos syndrome are associated with a significant increase of risk for aortic dissection. Entities that increase wall stress such as congenital bicuspid aortic valve, coarctation and hypertension are other factors that contribute to an increase in the incidence of the dissection. Pregnancy in the third trimester also has an increase incidence in dissection presumably due to the changes that occur to collagenous ligaments in pregnancy. About 50% of aortic dissections that occur in women under 40 are in women who are pregnant. Aortic dissection affects men more than women (2:1) with peak incidence in 6th and 7th decades.

Ninety five percent of dissections occur within a few centimeters of the aortic valve in the ascending aorta or just distal to the left subclavian artery.

There have been two classification systems with the Stanford system being more universally used.

Stanford Classification:

A- Involvement of ascending aorta

B – Involvement of aortic arch and distal aorta

 

Debakey Classification

Type I – ascending aorta, extends beyond the arch (30%)

Type II – ascending aorta only (20%)

Type III – descending aorta involving the thoracic aorta (50%)

Therapy is aimed at halting progression of the dissection.   Initially, blood pressure should be reduced to <100-120 mm Hg with an intravenous (IV) agents, such as nitroprusside or trimethaphan.

Treatment options are based on the position of the dissection.  If the dissection involves the ascending aorta, then emergency surgery is indicated because of the propensity for occlusion of the coronary artery, associated dysfunction of the aortic valve, and rupture into the pericardium.

If only the descending aorta is involved and there are no signs of distal ischemia, then medical management is indicated.

Ascending Aortic Dissection

06648 thoracic aorta thorax ascending aortic dissection Type A dissection CTscan Courtesy Ashley Davidoff MD

Descending Thoracic Aortic  Dissection

The digital angiogram in the LAO projection shows an intimal dissection starting just after the left subclavian artery. The true lumen is medial and smaller than the laterally and leftwardly placed larger false lumen. 35204 Courtesy Laura Feldman MD. code CVS artery aorta thorax thoracic descending dissection angiogram code aorta artery dissection flap.

Descending Thoracic Aorta  – Dissection

Gray scale US of the descending thoracic aorta showing a hypoechoic true lumen (black) and homogeneous echoes of the thrombosed lumen in this patient with aortic dissection. Courtesy Philips Medical Systems 33167

Descending Thoracic Aorta  – Dissection

Doppler US of the descending thoracic aorta showing flow in the true lumen (color) and no flow in the thrombosed lumen (gray echoes) in this patient with aortic dissection. Courtesy Philips Medical Systems 33166

Clinical

The clinical presentation is usually dramatic with hypercute “shearing” or “ripping “chest or back pain. Proximal Anterior chest pain is usually associated with tears of the ascending aorta, while dissection of the descending aorta usually give interscapular pain. Most patients are hypertensive. Findings on examination include aortic insufficiency (50%), pulse deficits (50% – commonly involve the brachiocephalic vessels) or neurologic manifestations Distal dissections may reveal pulse deficits of the left subclavian or femoral vessels

Diagnostic Tools

The radiologic diagnosis is often suspected on the plain film with the widened mediastinum and more specifically a blunted aortic knob or thickening of the wall of the knob more than 5 mm past the calcified aortic intima (Ring sign). CT, MRI and trans-esophageal echocardiography are all used with highsensitivity and specificty. TEE sensitivity/specificity of 99/98% Aortic angiography is an invasive procedure but may be best at delineating the extent of dissection

Dissection Involving the Ascending and Descending Aorta

20448 descending aorta ascending aorta fx dissection fx crescent dx aortic dissection type A CTscan Courtesy Ashley Davidoff MD DB

Type B dissection involving descending thoracic and abdominal aorta

24588 thorax abdomen fx dissection true lumen false lumen occluded renal artery angiogram angiography Courtesy Ashley Davidoff MD

Chronic Aortic Dissection

31262 hx 75 male with abdominal pain abdomen abdominal AAA aneurysm fx mural calcification thrombosed aortic dissection chronic dissection CTscan Davidoff MD

Rupture

Ruture of the Ascending Aorta

81F presents with acute shearing back pain and hypotension thorax thoracic aorta ascending aorta fx focal dissection rupture pericardium mediastinum fluid blood pericardial effusion hemopericardium azygous vein fx reflux dx aortic dissection with pericardial tamponade imaging radiology CTscan   Courtesy Ashley Davidoff MD 22343bduos500 hx

Treatment

Therapy is aimed at halting progression of the dissection Initially blood pressure should be reduced to <100-120 mm Hg with an IV agents such as nitroprusside or trimethaphan A decrease in the dV/dt (LV ejection velocity) should be done with beta-blockers Definitive treatment can be medical or surgical Surgical results are superior in acute proximal dissections (80% survival) and medical therapy may be advantageous in uncomplicated distal dissections (80% survival) For acute distal dissections complicated by vital organ compromise, rupture, aortic regurgitation or extension into the ascending aorta, surgery is also warranted Stable, isolated arch dissections and stable chronic dissections can be treated medically

Web References

eMedicine dissection

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